The use of connection-oriented networks to interconnect data users is becoming increasingly prevalent. As used herein, connection-oriented networks include networks transporting voice, video, data, and the like. Connection-oriented networks can use both real and virtual circuits. One popular arrangement for transmitting data over these networks is the asynchronous transfer mode (“ATM”) that transmits data between users as a series of 53 byte cells. Using ATM and other packet-oriented data transmission systems, such as frame relay, the connections between users are over virtual circuits. A virtual circuit is a path for transporting packets between users of the network. Most virtual circuits specify end points and let the network determine the path of the data. In many cases, the connections are permanent virtual circuits (“PVCs”).
Virtual circuits allow networks to realize “statistical multiplexing” in that when the virtual circuit is not sending data, the capacity can be used by other virtual circuits that share the link, or trunk. Virtual circuits, however, differ from dedicated lines. First, because their bandwidth is not dedicated, virtual circuits may be offered more cheaply. Second, virtual circuits offer the ability to transport or carry bursts of packets for short periods above the sustained bandwidth capabilities of the network. Bursts do not necessarily cause congestion on the lines.
Permanent virtual circuits remain up for an extended period of time. Most or all of the PVCs are protected in case of a failure condition. During a failure condition, the network attempts to establish an alternate path for the PVCs. Non-availability of links and nodes in a packet-based network can occur for several reasons, including congestion, failures at the links or nodes, or busy processors that have time-outs that expire. When a link or node is unavailable, the network may respond by rerouting the packets to the destination over other links, or trunks. The rerouting may be done according to known protocols within the network. These protocols, however, can lead to more congestion on the network because data packets may be placed on lines that are already congested.